This invention relates to the chemical processing of hydrocarbonaceous fluid feeds containing suspended solids and more particularly to processing hydrocarbonaceous feedstocks under hydrocarbon conversion conditions in packed bed reactors. Packed bed reactors are employed in a number of industries for converting fluid feedstocks. The packing can be reactive material, catalytic material, or inert material and can also act as deposition sites for reactants or products.
Plugging problems can occur when packed bed reactors are used to process fluids which contain suspended solids. Plugging is manifested by an unacceptable pressure drop across the reactor causing premature shutdown, for example, the shutdown of catalytic reactors while usable catalytic activity remains. Granular filter media are used in many industries for the removal of contaminants from liquids.
However, temperatures and pressures, flow velocities, viscosities, fluid properties, and catalyst and suspended solid composition and size distributions are so unique to petroleum refinery processing that unique solutions are sought. For example, while some industries are interested in providing liquids of great clarity, thereby requiring filter techniques for the removal of suspended solids even smaller than 10 microns in diameter, such techniques and filter designs have no application in petroleum refinery packed bed reactor technology where suspended solids of 10 microns in diameter or less cannot plug a reactor containing, for example, catalyst particles of 1/8 inch in diameter.
However, plugging can be particularly troublesome in downflow packed bed reactors. In the hydrocarbon processing industry, plugging is often encountered in downflow reactors that employ catalysts about 1/8 inch in diameter or less, e.g., 1/32 to 3/32 inch in diameter.
One technique used in the hydrocarbon processing industry is to employ one or more guard beds above active catalyst particles in order to protect the catalyst from incoming solids in the feed. Such guard beds have had only limited success, however. Even when multiple guard beds are used, catalytic reactors often experience unacceptable plugging, causing premature shutdown. Particularly troublesome is the uneven capture of solids in the guard bed leading to high local concentrations of solids.
One guard bed configuration is described in U.S. Pat. No. 3,562,800 wherein layers of 1/2 inch and 1/4 inch aluminum balls are used above a 1/32 inch catalyst bed. The depths of the beds are unspecified, however. Table 1 depicts several guard bed sequences which have been used for downflow packed catalyst beds in the hydrocarbon processing industry.
TABLE 1 ______________________________________ Particle Depth Diameters Configuration (inches) (inches) Type ______________________________________ A 6-12 1/2-3/4 spheres B 6 11/2 saddles 6 1/2-3/4 spheres C 12 1/4 rings 24 3/16 tablets 24 1/5 trilobes D 12 1/3 spheres 12 1/6 spheres E 4 1/2 saddles 3 3/4 spheres 3 1/2 spheres 3 1/4 spheres 4 1/2 saddles ______________________________________